Samuel Adams wrote to James Warren, "I could wish, if we must have abundant Addresses to see the manly Simplicity of Barckly the Quaker in his Dedication to Charles the 2d of England. Excepting that Instance, I do not recollect ever to have seen an Address to a Great Man, that was not more or less, and very often deeply, tincturd with Flattery."
In the opening of his Apology for the True Christian Divinity (1676), Robert Barclay featured an address to England's King Charles II. Barclay acknowledged that Charles II ordered the release of hundreds of Quakers from English jails. Barclay also stated that false accusations against the Quakers originated with people claiming to speak for the king, but not the monarch himself. Other than these acknowledgments, Barclay's address possesses the "simplicity" Adams admired. In his explanation ("apology") of Quaker belief, Barclay simply presented Charles II with the doctrines of the Society of Friends (Quakers).
Samuel Adams read the statement of Quaker belief and admired the author's simplicity of expression. Joseph Crukshank published Barclay's Apology in Philadelphia in 1775.
On Sept. 5, 1774, either Thomas Cushing of Massachusetts proposed (though Abraham Clark of New Jersey also claimed credit for the motion) that daily sessions of the Continental Congress open with prayer. John Jay of New York and John Rutledge of South Carolina objected to the motion, claiming the religious diversity of Congress made the measure impractical. Adams defended the measure by remarking, "I am not bigot. I can hear a prayer from a man of piety and virtue, who is at the same time a friend of his country."
Adams, a stranger to Philadelphia, nonetheless heard favorable accounts of Episcopalian (Anglican) pastor, the Rev. Jacob Duche. Adams's motion carried. Shortly after the Declaration of Independence, Duche defected to the British. In his place, a Presbyterian minister, Rev. George Duffield, and an Episcopalian pastor, Rev. William White. Duffield and White served as chaplains to Congress until 1784.
Derek Davis, Religion and the Continental Congress, 1774-1789: Contributions to Original Intent(New York: Oxford University Press, 2000), pages 73-76.